Caution: Killing Germs May Be Hazardous to Your Health

Behold yourself, for a moment, as an organism. A trillion cells stuck together, arrayed into tissues and organs and harnessed by your DNA to the elemental goals of survival and propagation. But is that all? An electron microscope would reveal that you are teeming with other life-forms. Any part of your body that comes into contact with the outside world—your skin, mouth, nose and (especially) digestive tract—is home to bacteria, fungi and protozoa that outnumber the cells you call your own by 10, or perhaps a hundred, to one.

Their ancestors began colonizing you the moment you came into the world, inches from the least sanitary part of your mother's body, and their descendants will have their final feast on your corpse, and join you in death. There are thousands of different species, found in combinations "as unique as our DNA or our fingerprints," says Stanford biologist David Relman, who is investigating the complex web of interactions microbes maintain with our digestive, immune and nervous systems. Where do you leave off, and they begin? Microbes, Relman holds, are "a part of who we are."

Relman is a leader in rethinking our relationship to bacteria, which for most of the last century was dominated by the paradigm of Total Warfare. "It's awful the way we treat our microbes," he says, not intending a joke; "people still think the only good microbe is a dead one." We try to kill them off with antibiotics and hand sanitizers. But bacteria never surrender; if there were one salmonella left in the world, doubling every 30 minutes, it would take less than a week to give everyone alive diarrhea. In the early years of antibiotics, doctors dreamed of eliminating infectious disease. Instead, a new paper in The Journal of the American Medical Association reports on the prevalence of Methicillinresistant Staphylococcus aureus (MRSA), which was responsible for almost 19,000 deaths in the United States in 2005—about twice as many as previously thought, and more than AIDS. Elizabeth Bancroft, a leading epidemiologist, called this finding "astounding."

As antibiotics lose their effectiveness, researchers are returning to an idea that dates back to Pasteur, that the body's natural microbial flora aren't just an incidental fact of our biology, but crucial components of our health, intimate companions on an evolutionary journey that began millions of years ago. The science writer Jessica Snyder Sachs summarizes this view in four words in the title of her ground-breaking new book: "Good Germs, Bad Germs." Our microbes do us the favor of synthesizing vitamins right in our guts; they regulate our immune systems and even our serotonin levels: germs, it seems, can make us happy. They influence how we digest our food, how much we eat and even what we crave. The genetic factors in weight control might reside partly in their genes, not ours. Regrettably, it turns out that bacteria exhibit a strong preference for making us fat.

Our well-meaning war on microbes has, by the relentless process of selection, toughened them instead. When penicillin began to lose its effectiveness against staph, doctors turned to methicillin, but then MRSA appeared—first as an opportunistic infection among people already hospitalized, now increasingly a wide-ranging threat that can strike almost anyone. The strain most commonly contracted outside hospitals, dubbed USA300, comes armed with the alarming ability to attack immune-system cells. Football players seem to be especially vulnerable: they get scraped and bruised and share equipment while engaging in prolonged exercise, which some researchers believe temporarily lowers immunity. In the last five years outbreaks have plagued the Cleveland Browns, the University of Texas and the University of Southern California, where trainers now disinfect equipment almost hourly. The JAMA article was a boon to makers of antimicrobial products, of which about 200 have been introduced in the United States so far this year. Press releases began deluging newsrooms, touting the benefits of antibacterial miracle compounds ranging from silver to honey. Charles Gerba, a professor of environmental microbiology at the University of Arizona, issued an ominous warning that teenagers were catching MRSA by sharing cell phones. Gerba is a consultant to the makers of Purell hand sanitizer, Clorox bleach and the Oreck antibacterial vacuum cleaner, which uses Microban to kill germs on your rug.

To be sure, MRSA is a scary infection, fast-moving and tricky to diagnose. Hunter Spence, a 12-year-old cheerleader from Victoria, Texas, woke up one Sunday in May with pain in her left leg. "I think I pulled a calf muscle," she told her mother, Peyton. By the next day, the pain was much worse and she was running a low-grade fever, but there was no other sign of infection. A doctor thought she might have the flu. By Wednesday her fever was 103 and the leg pain was unbearable. But doctors at two different community hospitals couldn't figure out what was wrong until Friday, when a blood culture came up positive for MRSA. By the time she arrived at Driscoll Children's Hospital in Corpus Christi—by helicopter—her temperature was 107 and her pulse 220. Doctors put her chance of survival at 20 percent.